Search process for physical downlink control channels in a communication system

ABSTRACT

Provided are methods and apparatuses for a user equipment to decode over a first set of resources a Physical Downlink Control CHannel (PDCCH) of a first type and to decode over a second set of resources a PDCCH of a second type in a same transmission time interval, to perform a first search process for candidate PDCCHs of the first type over a first set of resources and to perform a second search process for candidate PDCCHs of the second type over a second set of resources, and to determine whether to include for data reception resources that are separately indicated for potential transmission of PDCCHs of the first or of the second type.

PRIORITY

The present application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Applications No. 61/552,846 and No. 61/644,144 which werefiled in the United States Patent and Trademark Office on Oct. 28, 2011,and on May 8, 2012, respectively, the entire content of each of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to wireless communicationsystems and, more specifically, to transmission and reception ofphysical downlink control channels.

2. Description of the Art

A communication system includes a DownLink (DL) that conveystransmission signals from transmission points such as Base Stations(BSs) or NodeBs to User Equipments (UEs) and an UpLink (UL) that conveystransmission signals from UEs to reception points such as NodeBs. A UE,also commonly referred to as a terminal or a mobile station, may befixed or mobile and may be a cellular phone, a personal computer device,etc. A NodeB, which is generally a fixed station, may also be referredto as an access point or other equivalent terminology.

DL signals includes data signals, which carry information content,control signals, and Reference Signals (RS), which are also known aspilot signals. A NodeB conveys data information to UEs throughrespective Physical Downlink Shared CHannels (PDSCHs) and controlinformation through respective Physical Downlink Control CHannels(PDCCHs). UL signals also include data signals, control signals and RS.UEs convey data information to NodeBs through respective Physical UplinkShared CHannels (PUSCHs) and control information through respectivePhysical Uplink Control CHannels (PUCCHs). A UE transmitting datainformation may also convey control information through a PUSCH.

Downlink Control Information (DCI) serves several purposes and isconveyed through DCI formats in respective PDCCHs. For example, DCIincludes DL Scheduling Assignments (SAs) for PDSCH receptions and UL SAsfor PUSCH transmissions. As PDCCHs are a major part of a total DLoverhead, the required resources required to transmit PDCCHs directlyreduce DL throughput. One method for reducing PDCCH overhead is to scaleits size according to the resources required to transmit the DCI formatsduring a DL Transmission Time Interval (TTI). When Orthogonal FrequencyDivision Multiple (OFDM) is used as a DL transmission method, a ControlChannel Format Indicator (CCFI) parameter transmitted through a PhysicalControl Format Indicator CHannel (PCFICH) can be used to indicate anumber of OFDM symbols occupied by PDCCHs in a DL TTI.

FIG. 1 is a diagram illustrating a conventional structure for PDCCHtransmissions in a DL TTI.

Referring to FIG. 1, a DL TTI includes one subframe having N=14 OFDMsymbols. A DL control region that includes PDCCH transmissions occupiesa first M OFDM symbols 110. A remaining N-M OFDM symbols are usedprimarily for PDSCH transmissions 120. A PCFICH 130 is transmitted insome sub-carriers, also referred to as Resource Elements (REs), of afirst OFDM symbol and includes 2 bits indicating a DL control regionsize of M=1, or M=2, or M=3 OFDM symbols. Moreover, some OFDM symbolsalso contain respective RS REs, 140 and 150. These RS are transmittedsubstantially over an entire DL operating BandWidth (BW) and arereferred to as Common RS (CRS), as they can be used by each UE to obtaina channel estimate for its DL channel medium and to perform othermeasurements. The BW unit for a PDSCH or a PUSCH over a subframe isreferred to as a Physical Resource Block (PRB). A PRB includes severalREs, such as for example 12 REs.

Additional control channels may be transmitted in a DL control region,but are not shown for brevity. For example, when using a HybridAutomatic Repeat reQuest (HARQ) process for data transmission in aPUSCH, a NodeB may transmit HARQ-ACKnowledgement (ACK) information in aPhysical Hybrid-HARQ Indicator CHannel (PHICH) to indicate to a UEwhether its previous transmission of each data Transport Block (TB) in aPUSCH was correctly received (i.e., through an ACK) or incorrectlyreceived (i.e., through a Negative ACK (NACK)).

In addition to the CRS in FIG. 1, other DL RS types are the DeModulationRS (DMRS), which may only be transmitted in PRBs used for a PDSCHtransmission.

FIG. 2 is a diagram illustrating a conventional DMRS structure.

Referring to FIG. 2, DMRS REs 210 and 215 in a PRB convey DMRS from fourAntenna Ports (APs). A DMRS transmission from a first AP applies anOrthogonal Covering Code (OCC) of {1, 1} 220 over two DMRS REs locatedin a same frequency position and are successive in the time domain,while a second AP applies an OCC of {1, −1} 225. A DMRS transmissionfrom a third AP is in different REs than DMRS transmissions from a firstAP, and the third AP applies an OCC of {1, 1} 230 over two DMRS REslocated in a same frequency position and are successive in the timedomain, while a fourth AP applies an OCC of {1, −1} 235. A UE receivercan estimate a channel experienced by a signal from an AP by removing arespective OCC at respective DMRS Res, and may also possibly estimatethe channel by interpolating across respective DMRS REs in a subframe.

FIG. 3 is a diagram illustrating a conventional encoding process for aDCI format.

Referring to FIG. 3, a NodeB separately codes and transmits each DCIformat in a respective PDCCH. A Radio Network Temporary Identifier(RNTI) for a UE, for which a DCI format is intended for, masks a CyclicRedundancy Check (CRC) of a DCI format codeword in order to enable theUE to identify that a particular DCI format is intended for the UE. TheCRC of (non-coded) DCI format bits 310 is computed using a CRCcomputation operation 320, and the CRC is then masked using an exclusiveOR (XOR) operation 330 between CRC and RNTI bits 340. The XOR operation330 is defined as: XOR(0,0)=0, XOR(0,1)=1, XOR(1,0)=1, XOR(1,1)=0. Themasked CRC bits are appended to DCI format information bits using a CRCappend operation 350, channel coding is performed using a channel codingoperation 360 (e.g. an operation using a convolutional code), followedby rate matching operation 370 applied to allocated resources, andfinally, an interleaving and modulation 380 operation is performed, andthe output control signal 390 is transmitted. In the present example,both a CRC and a RNTI include 16 bits.

FIG. 4 is a diagram illustrating a conventional decoding process for aDCI format.

Referring to FIG. 4, a UE receiver performs the reverse operations of aNodeB transmitter to determine whether the UE has a DCI formatassignment in a DL subframe. A received control signal 410 isdemodulated and the resulting bits are de-interleaved at operation 420,a rate matching applied at a NodeB transmitter is restored throughoperation 430, and data is subsequently decoded at operation 440. Afterdecoding the data, DCI format information bits 460 are obtained afterextracting CRC bits 450, which are then de-masked 470 by applying theXOR operation with a UE RNTI 480. Finally, a UE performs a CRC test 490.If the CRC test passes, a UE determines that a DCI format correspondingto the received control signal 410 is valid and determines parametersfor signal reception or signal transmission. If the CRC test does notpass, a UE disregards the presumed DCI format.

To avoid a PDCCH transmission to a UE that is blocking a PDCCHtransmission to another UE, a location of each PDCCH in thetime-frequency domain of a DL control region is not unique. Therefore, aUE must perform multiple decoding operations to determine whether thereare PDCCHs intended for the UE in a DL subframe. The REs carrying aPDCCH are grouped into Control Channel Elements (CCEs) in the logicaldomain. For a given number of DCI format bits in FIG. 2, a number ofCCEs for a respective PDCCH depends on a channel coding rate (in thepresent example, a Quadrature Phase Shift Keying (QPSK) is used as themodulation scheme). A NodeB may use a lower channel coding rate (i.e.,more CCEs) for transmitting PDCCHs to UEs experiencing a low DLSignal-to-Interference and Noise Ratio (SINR) than to UEs experiencing ahigh DL SINR. The CCE aggregation levels may include, for example, 1, 2,4, and 8 CCEs.

For a PDCCH decoding process, a UE may determine a search space forcandidate PDCCHs after the UE restores the CCEs in the logical domainaccording to a common set of CCEs for all UEs (i.e., a Common SearchSpace (CSS)) and according to a UE-dedicated set of CCEs (i.e., aUE-Dedicated Search Space (UE-DSS)). A CSS may include the first C CCEsin the logical domain. A UE-DSS may be determined according to apseudo-random function having UE-common parameters as inputs, such asthe subframe number or the total number of CCEs in the subframe, andUE-specific parameters such as the RNTI. For example, for CCEaggregation levels Lε{1,2,4,8}, the CCEs corresponding to PDCCHcandidate in are given by Equation (1).

CCEs for PDCCH candidate m=L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  ( )

In Equation (1), N_(CCE,k) is the total number of CCEs in subframe k,i=0, . . . , L−1, m=0, . . . , M^((L))−1, and M^((L)) is the number ofPDCCH candidates to monitor in the search space. Exemplary values ofM^((L)) for Lε{1,2,4,8} are, respectively, {6, 6, 2, 2}. For the UE-CSS,Y_(k)=0. For the UE-DSS, Y_(k)=(A·Y_(k-1))mod D where Y₁=RNTI≠0, A=39827and D=65537.

DCI formats conveying information to multiple UEs are transmitted in aCSS. Additionally, if enough CCEs remain after the transmission of DCIformats conveying information to multiple UEs, a CSS may also conveysome UE-specific DCI formats for DL SAs or UL SAs. A UE-DSS exclusivelyconveys UE-specific DCI formats for DL SAs or UL SAs. For example, aUE-CSS may include 16 CCEs and support 2 DCI formats with L=8 CCEs, or 4DCI formats with L=4 CCEs, or 1 DCI format with L=8 CCEs and 2 DCIformats with L=4 CCEs. The CCEs for a CSS are placed first in thelogical domain (prior to interleaving).

FIG. 5 is a diagram illustrating a conventional transmission process ofa DCI format in a respective PDCCH.

Referring to FIG. 5, after channel coding and rate matching is performed(as described with reference to FIG. 3), encoded DCI format bits aremapped, in the logical domain, to CCEs of a PDCCH. The first 4 CCEs(L=4), CCE1 501, CCE2 502, CCE3 503, and CCE4 504 are used for PDCCHtransmission to UE1. The next 2 CCEs (L=2), CCE5 511 and CCE6 512, areused for PDCCH transmission to UE2. The next 2 CCEs (L=2), CCE7 521 andCCE8 522, are used for PDCCH transmission to UE3. Finally, the last CCE(L=1), CCE9 531, is used for PDCCH transmission to UE4.

The DCI format bits are then scrambled, at step 540, by a binaryscrambling code, and the scrambled bits are modulated at step 550. EachCCE is further divided into Resource Element Groups (REGs). For example,a CCE including 36 REs can be divided into 9 REGs that each include 4REs. In step 560, interleaving is applied among REGs in blocks of fourQPSK symbols. For example, a block interleaver may be used whereinterleaving is performed on symbol-quadruplets (i.e., four QPSK symbolscorresponding to the four REs of a REG) instead of on individual bits.After interleaving the REGs, in step 570, a resulting series of QPSKsymbols may be shifted by J symbols, and finally, in step 580, each QPSKsymbol is mapped to an RE in a DL control region. Therefore, in additionto RSs from NodeB transmitter antennas 591 and 592, and other controlchannels, such as a PCFICH 593 and a PHICH (not shown), REs in a DLcontrol region contain QPSK symbols for PDCCHs corresponding to DCIformats for UE1 594, UE2 595, UE3 596, and UE4 597.

The control region for transmissions of PDCCHs in FIG. 5 uses a maximumof M=3 OFDM symbols and transmits a control signal substantially over atotal operating DL BW. As a consequence, the control region has limiteda capacity and cannot achieve interference coordination in the frequencydomain. There are several cases where expanded capacity or interferencecoordination in the frequency domain is needed for transmission ofcontrol signals. One such case is a communication system with cellaggregation where the DL SAs or UL SAs to UEs in multiple cells aretransmitted in a single cell (for example, because other cells mayconvey only PDSCH). Another case is extensive use of multi-UE spatialmultiplexing of PDSCHs where multiple DL SAs correspond to same PDSCHresources. Another case is when DL transmissions from a first NodeBexperience strong interference from DL transmissions from a second NodeBand DL interference co-ordination in the frequency domain between thetwo NodeBs is needed.

Due to REG-based transmission and interleaving of PDCCHs, the controlregion cannot be expanded to include more OFDM symbols while maintainingcompatible operation with existing UEs that cannot be aware of suchexpansion. An alternative is to extend the control region in the PDSCHregion and use individual PRBs for transmitting new PDCCHs, which willbe referred to as Enhanced PDCCHs (E-PDCCHs). A NodeB may configure a UEto perform decoding operations for either or both of PDCCH and E-PDCCHs.Typically, a NodeB configures to a UE a functionality by higher layersignaling such as Radio Resource Control (RRC) signaling.

FIG. 6 is a diagram illustrating a conventional E-PDCCH transmissionstructure.

Referring to FIG. 6, although E-PDCCH transmissions start immediatelyafter PDCCH transmissions 610 and are transmitted over all remaining DLsubframe symbols, the E-PDCCH transmissions may instead start at apredetermined subframe symbol and extend over a part of remaining DLsubframe symbols. E-PDCCH transmissions may occur in four PRBs, 620,630, 640, and 650, while remaining PRBs 660, 662, 664, 666, 668 may beused for PDSCH transmissions. As an E-PDCCH transmission over a givennumber of subframe symbols may require fewer REs than the number ofsubframe symbols available in a PRB, multiple E-PDCCHs may bemultiplexed in a same PRB. The multiplexing can be in any combination ofpossible domains (i.e., time domain, frequency domain, or spatialdomain) and, in a manner similar to a PDCCH, an E-PDCCH includes atleast one Enhanced CCE (E-CCE).

An E-PDCCH transmission may be in a single PRB if a NodeB has accurateinformation for a channel experienced by a respective UE and can performFrequency Domain Scheduling (FDS) or beam-forming. Otherwise, TheE-PDCCH transmission can be in multiple PRBs. In the latter case, if aNodeB has multiple transmitter antennas, the NodeB may transmit anE-PDCCH using antenna transmission diversity. Herein, an E-PDCCHtransmitted in a single PRB is referred to as localized ornon-interleaved, while an E-PDCCH transmitted in multiple PRBs isreferred to as distributed or interleaved. Several aspects for anoperation with interleaved E-PDCCHs or with non-interleaved E-PDCCHsneed to be defined in order to provide a functional design. One aspectis the search process a UE performs to detect non-interleaved E-PDCCHsor to detect interleaved E-PDCCHs in a subframe. Another aspect is thedetection of interleaved E-PDCCHs and of non-interleaved E-PDCCHs by asame UE in a same subframe. Another aspect is the treatment by a UE ofPRBs configured to the UE for potential transmissions of interleavedE-PDCCHs or of non-interleaved E-PDCCHs when these PRBs are indicated tothe UE for a PDSCH reception.

Therefore, there is a need to define a process for a UE to search forand decode non-interleaved E-PDCCHs and interleaved E-PDCCHs in asubframe.

There is also a need to define a method for a UE to decode bothinterleaved E-PDCCHs and non-interleaved E-PDCCHs in a same subframe.

There is also a need to determine rules for the treatment by a UE ofPRBs configured to the UE for potential transmissions of interleavedE-PDCCHs or of non-interleaved E-PDCCHs when these PRBs are indicated tothe UE for a PDSCH reception.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to address at leastthe aforementioned limitations and problems, and the present inventionprovides methods and apparatus for a UE to perform decoding operationsfor candidate interleaved E-PDCCHs and for candidate non-interleavedE-PDCCHs in a same subframe, to perform a first search process forcandidate interleaved E-PDCCHs and a second search process for candidatenon-interleaved E-PDCCHs, and to determine whether to include for datareception respective REs in a PRB indicated for a PDSCH reception butalso separately indicated for potential transmissions of interleavedE-PDCCHs or of non-interleaved E-PDCCHs.

According to an aspect of the present invention, a method for a UserEquipment (UE) to perform decoding operations for two types of PhysicalDownlink Control CHannels (PDCCHs), each PDCCH including at least oneControl Channel Element (CCE) and transmitted from a base station in aTransmission Time Interval (TTI), wherein a PDCCH of a first type istransmitted in a first set of resources and with an aggregation level ofCCEs selected from a first set of aggregation levels of CCEs and whereina PDCCH of a second type is transmitted in a second set of resources andwith an aggregation level of CCEs selected from a second set ofaggregation levels of CCEs is provided. The method includes signaling,by the base station, to the UE, the first set of resources and theassociated first PDCCH type and the second set of resources and theassociated second PDCCH type; decoding, by the UE, for each aggregationlevel of CCEs in the first set of aggregation levels of CCEs, arespective number of candidate PDCCHs of the first type in the first setof resources; and decoding, by the UE, for each aggregation level ofCCEs in the second set of aggregation levels of CCEs, a respectivenumber of candidate PDCCHs of the second type in the second set ofresources.

According to another aspect of the present invention, a method for aUser Equipment (UE) to determine locations for M candidate PhysicalDownlink Control CHannels (PDCCHs) in a set of N Physical ResourceBlocks (PRBs) in a Transmission Time Interval (TTI), a candidate PDCCHincluding an aggregation level of Control Channel Elements (CCEs), the Mcandidate PDCCHs being used for a same aggregation level of CCEs isprovided. The method includes determining a location for each of the Mcandidate PDCCHs in a different PRB if N is greater than M; anddetermining a location for each of the first N candidate PDCCHs in adifferent PRB and determining a location for each of the remaining ifcandidate PDCCHs in a different PRB if M is greater than N and 2N isgreater than H.

According to another aspect of the present invention, a method for aUser Equipment (UE) to determine whether to include or omit, for datareception, respective Resource Elements (REs) in a reference PhysicalResource Block (PRB) included in a Resource Block Group (RBG) signaledto the UE by a base station through a Physical Downlink Control CHannel(PDCCH) for reception of a Physical Downlink Shared Channel (PDSCH) in aTransmission Time Interval (TTI), the reference PRB belonging to atleast one set of PRBs signaled to the UE by the base station forpotential transmission of at least one PDCCH in a TTI is provided. Themethod includes omitting, for data reception, REs in the reference PRB,if the PDCCH is of a first type and if the UE detects the PDCCH in PRBsin a set of PRBs that includes the reference PRB, or if the referencePRB is in a first set of PRBs, regardless of whether the PRBs where theUE detects the PDCCH include the reference PRB, or omitting for datareception REs in the reference PRB if the PDCCH is of a second type andthe UE detects the PDCCH in PRBs that include the reference PRB; andincluding, for data reception, REs in the reference PRB if the PDCCH isof a first type, the reference PRB is in a second set of PRBs, and theUE detects the PDCCH in PRBs in a first set of PRBs, or including, fordata reception, REs in the reference PRB if the PDCCH is of a secondtype and the UE detects the PDCCH in PRBs that do not include thereference PRB.

According to another aspect of the present invention, a User Equipment(UE) apparatus for performing decoding operations for two types ofPhysical Downlink Control CHannels (PDCCHs), each including at least oneControl Channel Element (CCE) and transmitted from a base station in aTransmission Time Interval (TTI), wherein a PDCCH of a first type istransmitted in a first set of resources and with an aggregation level ofCCEs selected from a first set of aggregation levels of CCEs and whereina PDCCH of a second type is transmitted in a second set of resources andwith an aggregation level of CCEs selected from a second set ofaggregation levels of CCEs is provided. The apparatus includes areceiver for receiving signaling from the base station informing of thefirst set of resources and the associated first PDCCH type and of thesecond set of resources and the associated second PDCCH type; a decoderfor decoding for each aggregation level of CCEs in the first set ofaggregation levels of CCEs a respective number of candidate PDCCHs ofthe first type in the first set of resources; and a decoder for decodingfor each aggregation level of CCEs in the second set of aggregationlevels of CCEs a respective number of candidate PDCCHs of the secondtype in the second set of resources.

According to another aspect of the present invention, a User Equipment(UE) apparatus for determining locations for M candidate PhysicalDownlink Control CHannels (PDCCHs) in a set of N Physical ResourceBlocks (PRBs) in a Transmission Time Interval (TTI), a candidate PDCCHincluding an aggregation level of Control Channel Elements (CCEs), the Mcandidate PDCCHs being used for a same aggregation level is provided.The apparatus includes a searcher for determining a location for each ofthe M candidate PDCCHs in a different PRB if M is less than or equal toN and for determining a location for each of the first N candidatePDCCHs in a different PRB and determining a location for each of theremaining if M-N candidate PDCCHs in a different PRB if M is greaterthan N and 2N is greater than M; and a decoder for decoding candidatePDCCHs.

According to another aspect of the present invention, a User Equipment(UE) apparatus for determining whether to include or omit for datareception respective Resource Elements (REs) in a reference PhysicalResource Block (PRB) included in a Resource Block Group (RBG) signaledto the UE apparatus by a base station through a Physical DownlinkControl CHannel (PDCCH) for reception of a Physical Downlink SharedChannel (PDSCH) in a Transmission Time Interval (TTI), the reference PRBbelonging to at least one set of PRBs signaled to the UE apparatus bythe base station for potential transmission of at least one PDCCH in aTTI is provided. The apparatus includes a decoder for detecting thePDCCH; a selector for omitting for data reception REs in the referencePRB if the PDCCH is of a first type and if the UE apparatus detects thePDCCH in PRBs in a set of PRBs that includes the reference PRB or if thereference PRB is in a first set of PRBs, regardless of whether the PRBswhere the UE apparatus detects the PDCCH include the reference PRB, oromitting for data reception REs in the reference PRB if the PDCCH is ofa second type and the UE apparatus detects the PDCCH in PRBs thatinclude the reference PRB, and for including for data reception REs inthe reference PRB if the PDCCH is of a first type, the reference PRB isin a second set of PRBs, and the UE apparatus detects the PDCCH in PRBsin a first set of PRBs or including for data reception REs in thereference PRB if the PDCCH is of a second type and the UE apparatusdetects the PDCCH in PRBs that do not include the reference PRB; and areceiver for receiving the PDSCH.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a conventional structure for PDCCHtransmissions;

FIG. 2 is a diagram illustrating a conventional DMRS structure.

FIG. 3 is a block diagram illustrating a conventional encoding processfor a DCI format;

FIG. 4 is a block diagram illustrating a conventional decoding processfor a DCI format;

FIG. 5 is a diagram illustrating a transmission process for PDCCHs;

FIG. 6 is a diagram illustrating a conventional use of PRBs for E-PDCCHtransmissions;

FIG. 7 is a diagram illustrating a process for allocating PRBs forinterleaved E-PDCCHs and PRBs for non-interleaved E-PDCCHs to a UEaccording to an embodiment of the present invention;

FIG. 8 is a diagram illustrating a determination of an E-CCE sizeaccording to whether a respective E-PDCCH is interleaved ornon-interleaved according to an embodiment of the present invention;

FIG. 9 is a diagram illustrating a determination of an E-CCE size for anon-interleaved E-PDCCH according to a number of assigned OFDM symbolsaccording to an embodiment of the present invention;

FIG. 10 is a diagram illustrating an assignment of separate number ofcandidates M_(E,D) ^((L) ^(E,D) ⁾ and M_(E,L) ^((L) ^(E,L) ⁾ per E-CCEaggregation level L_(E,D) and L_(E,L) for interleaved E-PDCCHs and fornon-interleaved E-PDCCHs, respectively, according to an embodiment ofthe present invention;

FIG. 11 is a diagram illustrating an assignment of non-interleavedE-PDCCH candidates to PRBs configured to a UE for non-interleavedE-PDCCHs according to an embodiment of the present invention; and

FIG. 12 is a diagram illustrating a process for a UE to determinewhether to use for PDSCH reception a PRB configured for E-PDCCH andincluded in an RBG indicated for PDSCH reception according to anembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Hereinafter, embodiments of the present invention are described withreference to the accompanying drawings. In the following description,the same elements may be designated by the same reference numeralsalthough they are shown in different drawings. Further, various specificdefinitions found in the following description are provided only to helpgeneral understanding of the present invention, and it is apparent tothose skilled in the art that the present invention can be implementedwithout such definitions. Further, in the following description of thepresent invention, a detailed description of known functions andconfigurations incorporated herein may be omitted when such adescription may obscure the subject matter of the present invention.

Additionally, although embodiments of the present invention aredescribed below with reference to Orthogonal Frequency DivisionMultiplexing (OFDM), embodiments of the present invention are alsoapplicable to all Frequency Division Multiplexing (FDM) transmissions ingeneral, including Discrete Fourier Transform (DFT)-spread OFDM.

The embodiments of the invention do not assume a particular structurefor E-PDCCH transmissions. Some generic aspects of E-PDCCH transmissionsaccording to embodiments of the present invention may include:

-   -   a) An E-PDCCH is transmitted in Enhanced CCEs (E-CCEs); an E-CCE        may or may not have a same size as a CCE; an E-CCE includes        E-REGs and an E-REG includes a number of REs in a PRB.    -   b) The number of OFDM symbols for transmitting E-PDCCHs in a        subframe may be all symbols remaining after PDCCH transmissions        or the number may be a number of OFDM symbols starting at a        predetermined OFDM symbol.    -   c) A PRB used for E-PDCCH transmissions may contain E-REGs or        E-CCEs used for transmitting different E-PDCCHs.    -   d) For interleaved E-PDCCHs, multiplexing of respective E-CCEs        over a number of PRBs and OFDM symbols may have a same structure        as for CCEs. A number of E-CCEs is computed in a same manner as        a number of CCEs over all available PRBs (BW and all available        OFDM symbols) in a subframe. E-REGs used for possible        transmissions of other control channels, such as E-PCFICH and        E-PHICH, are discounted.    -   e) For non-interleaved E-PDCCHs, E-REGs of respective E-CCEs in        a PRB may be multiplexed over a combination of possible domains        (time, frequency, or spatial domain) with E-REGs of E-CCEs for        other non-interleaved E-PDCCHs.    -   f) Demodulation of E-PDCCHs may be based on a RS transmitted        only in some OFDM symbols of PRBs used for transmitting        respective E-PDCCHs (DMRS).

A first example according to an embodiment of the present inventionconsiders the PRBs and the E-CCE size for interleaved E-PDCCHs and thePRBs and the E-CCE size for non-interleaved E-PDCCHs. A UE is informedby a NodeB of a set of PRBs where a respective interleaved E-PDCCH ornon-interleaved E-PDCCH transmission occurs. For non-interleavedE-PDCCHs, a set of PRBs is informed using higher layer signaling. Forinterleaved E-PDCCHs, a set of PRBs is informed either using higherlayer signaling or through an E-PCFICH that is transmitted over apredetermined set of PRBs used for interleaved E-PDCCHs and informs a UEof a total number of PRBs used for interleaved E-PDCCH transmissions ina same subframe.

FIG. 7 is a diagram illustrating a process for allocating PRBs forinterleaved E-PDCCHs and PRBs for non-interleaved E-PDCCHs to a UEaccording to an embodiment of the present invention.

Referring to FIG. 7, PRBs in subframe k are allocated for transmittingPDCCHs 710, PDSCHs 720, interleaved E-PDCCHs 730 and non-interleavedE-PDCCHs 740. Separate PRBs are configured to a UE for interleavedE-PDCCH and non-interleaved E-PDCCH transmissions. In subframe k+1, PRBsused for non-interleaved E-PDCCH transmissions in subframe k are usedfor PDSCH transmissions, 750A and 750B, while two additional PRBs, 760Aand 760B, are included for interleaved E-PDCCH transmissions. Theindication of the additional PRBs for interleaved E-PDCCH transmissionsis performed through a transmission of an E-PCFICH (not shown) over apredetermined number of OFDM symbols and in a minimum set of PRBs thatalways exist for transmitting interleaved E-PDCCHs to a UE.

A UE is configured by a NodeB to perform blind decoding operations in asame subframe for both interleaved E-PDCCHs and for non-interleavedE-PDCCHs. One reason a UE performs blind decoding operations for bothtypes of E-PDCCHs is to provide robustness when channel information fora UE at a NodeB is not reliable in some subframes. For example, whenchannel information feedback from a UE is not recent enough and thechannel may have changed since a last feedback, or when a NodeB deemsthat a feedback from a UE is not accurate (such as for example when asignal transmission from a UE experiences fading), an interleavedE-PDCCH transmission to the UE may be used. Another reason is for aNodeB to effectively multiplex E-PDCCHs to different UEs whileminimizing the associated resources. For example, as one PRB over allavailable OFDM symbols for E-PDCCH transmission may be too large toinclude only a single E-PDCCH, multiple non-interleaved E-PDCCHs may bemultiplexed in one PRB over all available OFDM symbols. However, if in agiven subframe only one such UE has a non-interleaved E-PDCCHtransmission, a NodeB may use the respective PRB for PDSCH transmissionand use an interleaved E-PDCCH transmission for that UE (e.g., insubframe k+1 of FIG. 7). Yet another reason is to enable a NodeB to uselarge E-CCE aggregation levels, which may be possible for interleavedE-PDCCHs but may not be possible for non-interleaved E-PDCCHs (as anon-interleaved E-PDCCH may be transmitted in one PRB).

In the present example, the E-CCE size is determined subject to anobjective of maintaining same E-CCE aggregation levels for E-PDCCHs asthe CCE aggregation levels for PDCCHs. Moreover, for non-interleavedE-PDCCHs, an additional objective is to support the possible E-CCEaggregation levels within one PRB over the number of OFDM symbols in asubframe that are available for E-PDCCH transmissions.

The above two objectives may require that an E-CCE size fornon-interleaved E-PDCCHs is different from an E-CCE size for interleavedE-PDCCHs. For example, an E-CCE size for interleaved E-PDCCHs may atleast equal to the CCE size, which may be equal, for example, to 36 REs.A reason for allowing a larger E-CCE size for interleaved E-PDCCHs thanthe CCE size is because, for a same DCI format size and a sameaggregation level with a same E-CCE/CCE size, a detection performancefor an interleaved E-PDCCH may be worse than a PDCCH one as demodulationfor the former is based on a DMRS and E-PDCCH transmission mayexperience reduced interference and frequency diversity whiledemodulation for the latter is based on a CRS and PDCCH transmission mayexperience maximum interference and frequency diversity. The DMRS mayprovide a worse channel estimate than the CRS if more CRS REs than DMRSREs can be assumed to be used by a UE for channel estimation. Therefore,allowing for a larger E-CCE size for an interleaved E-PDCCH transmissionthan the CCE size for a PDCCH transmission allows for a greater codinggain for an interleaved E-PDCCH transmission than for a PDCCHtransmission, for a same aggregation level, which can offset performancedegradation from a worse channel estimate or from reduced frequency andinterference diversity. Nevertheless, as the accuracy of channelestimates associated with interleaved E-PDCCH and PDCCH are often beassumed to be similar (e.g., at high SINRs), an E-CCE size forinterleaved E-PDCCH transmission may be same as the CCE size.

The E-CCE size for a non-interleaved E-PDCCH may be smaller than the CCEsize as due to FDS or beam-forming, a non-interleaved E-PDCCHtransmission may experience a higher SINR than a PDCCH transmission thatis substantially distributed over an entire operating BW. Moreover, forsame CCE and E-CCE aggregation levels for PDCCH and non-interleavedE-PDCCH transmissions, respectively, the E-CCE size is set such that aninteger number of E-CCEs fit within a PRB over the assigned number ofOFDM symbols with minimal, if any, empty REs. For example, for a PRBsize of 12 REs and 11 OFDM symbols assigned to non-interleaved E-PDCCHs,there are a total of 132 REs. Discounting 20 REs that may be assumed tobe used for RS transmissions of various types, the E-CCE size (i.e., thenumber of available REs for transmitting a non-interleaved E-PDCCH is asubframe) required to support aggregation levels up to 4 E-CCEs is(132-20)/4=28 REs. Therefore, for a PRB size of 12 REs and a maximum of14 OFDM symbol, although after excluding the 24 DMRS REs per PRB (suchas described with reference to FIG. 2) the number of REs available totransmit non-interleaved E-PDCCH is (14×12-24)=144 which for 4 E-CCEsper PRB leads to an E-CCE size of 36 REs, the actual E-CCE size can besmaller than 36 Res, once the presence of other signals (such as theCRS) or channels (such as PDCCHs) in some REs is considered. In thiscase, the maximum E-CCE aggregation level for a non-interleaved E-PDCCHin a PRB is constrained to be 4, while the maximum E-CCE aggregationlevel for an interleaved E-PDCCH can be same as for a PDCCH and equals8.

FIG. 8 is a diagram illustrating a determination of an E-CCE sizeaccording to whether a respective E-PDCCH is interleaved ornon-interleaved according to an embodiment of the present invention.

Referring to FIG. 8, an E-CCE size for a transmission of anon-interleaved E-PDCCH includes X REs 810, and this E-CCE size issmaller than an E-CCE size for a transmission of an interleaved E-PDCCHthat includes Y REs 820.

The E-CCE size (i.e., the number of REs available for transmittingE-PDCCH in an E-CCE of 36 REs) for a non-interleaved E-PDCCH may varyaccording to the number of OFDM symbols available for non-interleavedE-PDCCH transmissions. For example, discounting for REs that may beassumed to be used for RS transmissions of various types, the E-CCE sizefor a non-interleaved E-PDCCH in a PRB may be 28 Res, when 11 OFDMsymbols are used and may be 36 REs (which is equal to the CCE size),when 14 OFDM symbols are used. Using a larger E-CCE size will result inlower E-CCE aggregation levels being more frequently used, and a NodeBcan configure accordingly a number of candidates per E-CCE aggregationlevel. An E-CCE size for an interleaved E-PDCCH transmission is alwaysindependent of a number of assigned OFDM symbols that may only affectthe available number of such E-CCEs but not their size. The reverseapplies for the E-CCEs of a non-interleaved E-PDCCH.

FIG. 9 is a diagram illustrating a determination of an E-CCE size for anon-interleaved E-PDCCH according to a number of assigned OFDM symbolsaccording to an embodiment of the present invention.

Referring to FIG. 9, for non-interleaved E-PDCCH, an E-CCE includes XREs used to transmit an E-PDCCH when the E-PDCCH is transmitted over N₁OFDM symbols 910 and an E-CCE includes Y REs used to transmit an E-PDCCHwhen the E-PDCCH is transmitted over N₂ OFDM symbols 920 where X<Y forN₁<N₂. For an interleaved E-PDCCH, an E-CCE always includes Y Res,regardless of whether the duration of an E-PDCCH transmission is over N₁OFDM symbols 930 or over N₂ OFDM symbols 940.

A second example according to another embodiment of the presentinvention considers the definition of search spaces used by a UE todetermine a location of a potential E-PDCCH transmission in an expandedcontrol region. For the decoding process of an E-PDCCH transmission,whether interleaved or non-interleaved, a UE determines a search spacefor candidate E-PDCCHs in a same manner as for the decoding process of aPDCCH transmission after restoring the E-CCEs in the logical domain. AUE may be configured to monitor only E-PDCCHs or both E-PDCCHs andPDCCHs.

For the UE-DSS of E-PDCCH transmissions, the present example accordingto an embodiment of the present invention considers that a UE isassigned (by a NodeB through higher layer signaling of PRBs forinterleaved E-PDCCHs and of PRBs for non-interleaved E-PDCCHs aspreviously described) a first number of candidates M_(E,D) ^((L) ^(E,D)⁾ corresponding to E-CCE aggregation levels L_(E,D)ε{1,2,4,8} fordecoding interleaved E-PDCCHs and a second number of candidates M_(E,L)^((L) ^(E,L) ⁾ corresponding to E-CCE aggregation levelsL_(E,L)ε{1,2,4,8} for decoding non-interleaved E-PDCCHs. The number ofcandidates M_(E,L) ^((L) ^(E,L) ⁼⁸⁾ may always equal zero if up to 4E-CCEs are supported in a PRB for non-interleaved E-PDCCH transmissions.Alternatively, a UE may be assigned only a first number of candidatesM_(E,D) ^((L) ^(E,D) ⁾ or the second number of candidates M_(E,L) ^((L)^(E,L) ⁾ and may derive the other number subject to a condition thatM_(E,D) ^((L) ^(E,D) ⁾+M_(E,L) ^((L) ^(E,L) ⁾=M_(E) ^((L) ^(E) ⁾ whereM_(E) ^((L) ^(E) ⁾ is either predetermined in the system operation orderived by a UE using other signaling from a NodeB such as, for example,signaling for a number of candidates per CCE aggregation level for PDCCHdecoding, if any.

The number of E-PDCCH candidates per E-CCE aggregation level may differbetween interleaved and non-interleaved E-PDCCHs. For example, aspreviously mentioned, a non-interleaved E-PDCCH may be associated with aNodeB having information of the channel experienced by a UE atrespective PRBs and the NodeB may select a PRB where a non-interleavedE-PDCCH transmission to a UE has the highest SINR and may also applybeam-forming. As a result, a non-interleaved E-PDCCH transmission maytypically experience high SINR and require a low E-CCE aggregationlevel. The reverse may be true for an interleaved E-PDCCH transmission,which may be used when a NodeB only has information of an averagechannel experienced by the UE over an entire operating BW or no suchinformation at all. Therefore, non-interleaved E-PDCCH transmissions mayhave a greater percentage of candidates for low E-CCE aggregation levelsthan interleaved E-PDCCH transmissions. For example, for a UE configuredwith both interleaved and non-interleaved E-PDCCH transmissions, thenumber of interleaved E-PDCCH candidates for an aggregation level of oneE-CCE is zero or the number of non-interleaved E-PDCCH candidates for anaggregation level of eight E-CCEs is zero.

If a UE receives both an interleaved E-PDCCH and a non-interleavedE-PDCCH for PDSCH scheduling (or for PUSCH scheduling), the UE maydisregard both of them or consider only one according to a predefinedrule (for example, consider an interleaved E-PDCCH as valid and anon-interleaved E-PDCCH as invalid).

FIG. 10 is a diagram illustrating an assignment of separate number ofcandidates M_(E,D) ^((L) ^(E,D) ⁾ and M_(E,L) ^((L) ^(E,L) ⁾ per E-CCEaggregation level L_(E,D) and L_(E,L) for interleaved E-PDCCHs and fornon-interleaved E-PDCCHs, respectively, according to an embodiment ofthe present invention.

Referring to FIG. 10, in step 1010A, a NodeB configures a UE (through anassignment of PRBs for interleaved E-PDCCHs transmissions and of PRBsfor non-interleaved E-PDCCHs transmissions) with M_(E,D) ^((L) ^(E,D) ⁾candidates for respective L_(E,D) E-CCE aggregation levels forinterleaved E-PDCCH, and performs such a configuration with M_(E,L)^((L) ^(E,L) ⁾ candidates for respective L_(E,L) E-CCE aggregationlevels for non-interleaved E-PDCCH in step 1010B. In step 1020A, insubframe k, a UE performs M_(E,D) ^((L) ^(E,D) ⁾ decoding operations foreach respective L_(E,D) E-CCE aggregation level for interleaved E-PDCCHtransmissions, and performs M_(E,L) ^((L) ^(E,L) ⁾ decoding operationsfor each respective L_(E,L) E-CCE aggregation level for non-interleavedE-PDCCH transmissions in step 1020B. A NodeB may transmit, to a UE, bothan interleaved E-PDCCH (e.g., for a PDSCH reception) and anon-interleaved E-PDCCH (e.g., for a PUSCH transmission) in subframe k.

For an interleaved E-PDCCH, E-CCEs corresponding to candidate m aredefined according to Equation (2).

E-CCEs for E-PDCCH candidate m=L _(E,D)·{(Y _(k) ·m)mod └N _(E-CCE,k) /L_(E,D) ┘}+i  (2)

In Equation (2), N_(E-CCE,k) is the total number of E-CCEs in subframek, i=0, . . . , L_(E,D)−1 and m=0, . . . , M_(E,D) ^((L) ^(E,D) ⁾−1. Forexample, values of for L_(E,D)ε{1,2,4,8} are, respectively, {4, 4, 2,2}. As for the UE-DSS of PDCCH transmissions, Y_(k)=(A·Y_(k-1))mod Dwhere Y⁻¹=RNTI≠0, A=39827 and D=65537. Therefore, for interleavedE-PDCCHs, a UE determines a UE-DSS for decoding E-PDCCH candidates in asimilar manner as for decoding PDCCH candidates.

For E-CCEs of a non-interleaved E-PDCCH transmission, which areconfigured to occur in any of N_(PRB) PRBs, a different approach isrequired, as a non-interleaved E-PDCCH transmission is assumed to beconfined to one PRB. In order to fully exploit FDS, non-interleavedE-PDCCH candidates M_(E,L) ^((L) ^(E,L) ⁾ for each E-CCE aggregationlevel L_(E,L) should be distributed over as many PRBs as possible. IfM_(E,L) ^((L) ^(E,L) ⁾ is equal to a number of configured PRBs N_(PRB),each PRB contains exactly one E-PDCCH candidate for E-CCE aggregationlevel L_(E,L). If M_(E,L) ^((L) ^(E,L) ⁾ is less than N_(PRB), each PRBcontains only a single E-PDCCH candidate and candidate PRBs for anon-interleaved E-PDCCH transmission may be semi-statically configuredby higher layer signaling or may pseudo-randomly vary across subframesusing for example a pseudo-random function generating M_(E,L) ^((L)^(E,L) ⁾ values out of N_(PRB) values. If M_(E,L) ^((L) ^(E,L) ⁾ isgreater than N_(PRB) (but, for simplicity, less than or equal to2N_(PRB)), └M_(E,L) ^((L) ^(E,L) ⁾/N_(PRB)┘ non-interleaved E-PDCCHcandidates exist in each of N_(PRB) PRBs and remaining M_(E,L) ^((L)^(E,L) ⁾=└M_(E,L) ^((L) ^(E,L) ⁾/N_(PRB)┘·N_(PRB) E-PDCCH candidates maybe pseudo-randomly placed in N_(PRB) PRBs (one E-PDCCH candidate perPRB) using, for example, the previous pseudo-random function generatingM_(E,L) ^((L) ^(E,L) ⁾−└M_(E,L) ^((L) ^(E,L) ⁾/N_(PRB)┘·N_(PRB) valuesout of N_(PRB) values. A deterministic placement may also apply, forexample, starting from a PRB with a lowest index.

FIG. 11 is a diagram illustrating an assignment of non-interleavedE-PDCCH candidates to PRBs configured to a UE for non-interleavedE-PDCCHs according to an embodiment of the present invention.

Referring to FIG. 11, a UE determines whether M_(E,L) ^((L) ^(E,L)⁾≦N_(PRB), in step 1110. If M_(E,L) ^((L) ^(E,L) ⁾≦N_(PRB), each of theN_(PRB) PRBs contains at most one E-PDCCH candidate for E-CCEaggregation level L_(E,L), in step 1120. If, in step 1130, the UEdetermines that M_(E,L) ^((L) ^(E,L) ⁾<N_(PRB), respective PRBs may besemi-statically configured or may pseudo-randomly vary across subframes,in step 1140. If M_(E,L) ^((L) ^(E,L) ⁾>N_(PRB), └M_(E,L) ^((L) ^(E,L)⁾/N_(PRB)┘·N_(PRB) E-PDCCH candidates exist in each of N_(PRB) PRBs andremaining M_(E,L) ^((L) ^(E,L) ⁾−└M_(E,L) ^((L) ^(E,L)⁾/N_(PRB)┘·N_(PRB) E-PDCCH candidates are pseudo-randomly placed inN_(PRB) PRBs (one E-PDCCH candidate per PRB), in step 1150.

When a PRB (transmitted over OFDM symbols used for E-PDCCHtransmissions) contains more E-CCEs than an E-CCE aggregation levelL_(E,L) for an E-PDCCH candidate, a UE must also determine L_(E,L)E-CCEs among E-CCEs contained in a PRB. For example, when a PRB contains4 E-CCEs and one E-PDCCH candidate, a location is unique for L_(E,L)=4,but 6 different locations exist for L_(E,L)=2 and 4 different locationsexist for L_(E,L)=1. A search space per PRB for a non-interleavedE-PDCCH is then defined in a similar manner as a search space over allPRBs of the expanded control region for interleaved E-PDCCHs and E-CCEscorresponding to a non-interleaved E-PDCCH candidate m, as defined byEquation (3).

E-CCEs for E-PDCCH candidate m=L_(E,L)·{(Y _(k) +m)mod └N _(E-CCE-PRB,k)/L _(E,L) ┘}+i  (3)

In Equation (3), N_(E-CCE-PRB,k) is a total number of E-CCEs in a PRB insubframe k, i=0, . . . , L_(E,L)−1, m=0, . . . , M_(E,L) ^((L) ^(E,L)⁾−1. For example, values of M_(E,L) ^((L) ^(E,L) ⁾ for L_(E,L)ε{1,2,4,8} are {2, 2, 2, 0}, respectively.

The two above-described steps for defining a search space fornon-interleaved E-PDCCH transmissions may also be performed jointly. Forexample, using previous notations, E-CCEs for a non-interleaved E-PDCCHcandidate m may be defined according to Equation (4).

E-CCEs for E-PDCCH candidate m=

(Z _(k) +m)·N _(E-CCE,PRB,k) mod(N _(PRB,k) ·N _(E-CCE-PRB,k))+L_(E,L)·{(Y _(k) +c _(k)(n))mod └N _(E-CCE-PRB,k) /L _(E,L)┘} mod N_(E-CCE-PRB,k) +i  (4)

In Equation (4), Z_(k) is a random variable (similar to Y_(k), Z_(k),depending on a UE's RNTI and a subframe index k), c_(k)(n) is a counterof existing non-interleaved E-PDCCH candidates (for E-CCE aggregationlevel L_(E,L)) in PRB n and subframe k, and N_(PRB,k) is a number ofPRBs assigned to a UE for non-interleaved E-PDCCH transmissions insubframe k. For a given E-CCE aggregation level, the first term randomlyselects a first PRB for the first non-interleaved E-PDCCH candidate andsequentially continues across PRBs, wrapping around after the last PRB.For a given E-CCE aggregation level, the second term sequentially placesE-CCEs for additional E-PDCCH candidates in a selected PRB using thecounter c_(k)(n) to define the E-CCEs for the additional E-PDCCHcandidates in the PRB. The order of PRBs where the additional E-PDCCHcandidates are located is the same as the order of PRBs where theinitial E-PDCCH candidates are located (the first term selects the PRBsand the second term selects the E-CCEs in a PRB for an E-PDCCHcandidate).

For example, for L_(E,L)=2, M_(E,L) ⁽²⁾=6, N_(E-CCE-PRB,k)=4,N_(PRB,k)=4, Z_(k)=1, and Y_(k)=2, there areN_(E-CCE-PRB,k)·N_(PRB,k)=16 E-CCEs sequentially numbered from 0 to 15(4 E-CCEs per PRB with sequentially numbered PRBs) and non-interleavedE-PDCCH candidates are located in E-CCEs as:

Candidate{0,1,2,3,4,5}:E-CCEs{[4,5],[8,9],[12,13],[0,1],[6,7],[10, 11]}

In order to reduce signaling requirements for indicating resourcesallocated to a PDSCH transmission to a UE, a resource allocation can beset for a multiple of PRBs according to the operating BW. This multipleof PRBs is referred to as Resource Block Group (RBG). If an RBG containsat least one PRB allocated to E-PDCCH transmissions, a UE alwaysdiscards these PRBs from a scheduled PDSCH reception that includes therespective RBG if these PRBs are configured for interleaved E-PDCCHtransmissions in the set of PRBs the UE detects the interleaved E-PDCCHsince, due to the interleaving of E-PDCCH transmissions, these PRBs arelikely to contain an E-PDCCH transmission to at least one UE. Forexample, for a set of 8 PRBs configured to a UE for potentialtransmission of interleaved E-PDCCHs, the UE always does not include anyof these PRBs for data reception in respective RBGs of a PDSCH scheduledby a DCI format conveyed by an interleaved E-PDCCH detected in the setof 8 PRBs even when the UE detects the interleaved E-PDCCH in only 4 ofthe set of 8 PRBs. The same principle may apply for a set of 4 PRBs andan interleaved E-PDCCH the UE detects in only 2 PRBs of the set of 4PRBs.

Additionally, as illustrated in FIG. 7, a UE may be configured withmultiple sets of PRBs for interleaved E-PDCCH transmissions where afirst (primary) set is always used in a subframe, and at least a secondset is used if all interleaved E-PDCCH transmissions in the subframecannot be accommodated in the first set. Then, if the UE detects aninterleaved E-PDCCH in the second set of PRBs, the UE assumes that thefirst set of PRBs is also used for interleaved E-PDCCH transmissions (atleast to other UEs) and may omit for data reception PRBs from the firstset of PRBs when any of these PRBs is included in a respective RBGindicated for PDSCH reception. However, if in a subframe the UE detectsan interleaved E-PDCCH in the first set of PRBs conveying a DCI formatfor PDSCH reception in RBGs that include PRBs from the second set ofPRBs, the UE includes these PRBs for data reception in the PDSCH andassumes that the second set of PRBs is not used to transmit interleavedE-PDCCHs in the subframe.

Therefore, as illustrated in FIG. 7, the PRBs configured for a UE forinterleaved E-PDCCHs may vary per subframe, with the exception of afirst (minimum) set of PRBs a UE may assume as always being used forinterleaved E-DPCCH transmissions (unless re-configured) in a subframe.Then, a UE may always disregard, from a PDSCH reception, the PRBs in thefirst (minimum) set of PRBs, even if the PDSCH reception is scheduled bya non-interleaved E-PDCCH in a PRB not in the minimum set of PRBs(second set of PRBs) while the UE may include for PDSCH reception (if soindicated by a respective DCI format) PRBs in a second set of PRBsconfigured for interleaved E-PDCCHs when the UE detects an interleavedE-PDCCH in the first set of PRBs. The at least one PRB per RBG allocatedto E-PDCCH transmissions may be fixed in the system operation, such asthe last PRB in the RBG, or be configured by a NodeB, or pseudo-randomlyvary according to the RBG index or the subframe index, for example.

For PRBs configured for non-interleaved E-PDCCH transmissions, asmultiple E-PDCCH transmissions to multiple UEs may be contained in eachof these PRBs, a DCI format conveyed by a non-interleaved E-PDCCH mayexplicitly or implicitly indicate whether a UE should consider thesePRBs for PDSCH reception. For example, for an explicit indication, a DCIformat may contain an information element including 1 bit indicatingthat a UE should use these PRBs for PDSCH reception if the bit has thebinary value 0, and indicating that the UE should discard these PRBsfrom PDSCH reception if the bit has the binary value 1. As the E-PDCCHtransmission to a UE may dynamically switch from non-interleaved tointerleaved, all DCI formats, regardless of the E-PDCCH transmissionmode, may contain the indication of whether a PRB is used for E-PDCCHtransmission. As previously described herein, a UE is informed of thePRBs allocated to E-PDCCH transmissions either through higher layersignaling or, possibly for interleaved E-PDCCH transmissions, alsothrough an E-PCFICH.

FIG. 12 is a diagram illustrating a process for a UE to determinewhether to use for PDSCH reception a PRB configured for E-PDCCH andincluded in an RBG indicated for PDSCH reception according to anembodiment of the present invention.

Referring to FIG. 12, PDSCH reception is scheduled for a UE over an RBGincluding 3 PRBs, which include 1 PRB allocated for E-PDCCHtransmissions 1210. For PRBs allocated to interleaved E-PDCCHtransmissions 1220, a UE always disregards such PRBs when such PRBs areincluded in RBGs indicated for PDSCH reception 1230. For PRBs allocatedto non-interleaved E-PDCCH transmissions 1240, a UE disregards such PRBswhen such PRBs are included in RBGs indicated for PDSCH receptionaccording to an explicit or implicit indication in a DCI format conveyedby an E-PDCCH scheduling a PDSCH reception 1250.

An alternative for non-interleaved E-PDCCH transmissions is to alwaysassume that one of the possibly multiple UEs for which E-PDCCHtransmissions are in a same PRB has a PDSCH transmission in the RBGcontaining the PRB. Then, the PRB can always be assumed occupied and noadditional signaling through the E-PDCCH scheduling the PDSCH in the RBGis needed. Therefore, for a PRB configured for non-interleaved E-PDCCHsand included in an RBG indicated to a UE for PDSCH reception, the UEalways disregards this PRB when the UE includes the transmission of thenon-interleaved E-PDCCH scheduling the respective PDSCH (implicitindication); otherwise, if the UE does not detect this non-interleavedE-PDCCH in this PRB (in the set of PRBs configured to the UE forpotential non-interleaved E-PDCCH transmissions), the UE includes thisPRB for PDSCH reception.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for a User Equipment (UE) to performdecoding operations for two types of Physical Downlink Control CHannels(PDCCHs), each PDCCH including at least one Control Channel Element(CCE) and transmitted from a base station in a Transmission TimeInterval (TTI), wherein a PDCCH of a first type is transmitted in afirst set of resources and with an aggregation level of CCEs selectedfrom a first set of aggregation levels of CCEs and wherein a PDCCH of asecond type is transmitted in a second set of resources and with anaggregation level of CCEs selected from a second set of aggregationlevels of CCEs, the method comprising the steps of: signaling, by thebase station, to the UE, the first set of resources and the associatedfirst PDCCH type and the second set of resources and the associatedsecond PDCCH type; decoding, by the UE, for each aggregation level ofCCEs in the first set of aggregation levels of CCEs, a respective numberof candidate PDCCHs of the first type in the first set of resources; anddecoding, by the UE, for each aggregation level of CCEs in the secondset of aggregation levels of CCEs, a respective number of candidatePDCCHs of the second type in the second set of resources.
 2. The methodof claim 1, wherein for at least one aggregation level of CCEs, arespective number candidate PDCCHs of the first type is different than arespective number of candidates PDCCHs of the second type.
 3. The methodof claim 2, wherein the highest aggregation level of CCEs with arespective number of candidates PDCCHs of the first type that is greaterthan zero is greater than the highest aggregation level of CCEs with arespective number of candidates PDCCHs of the second type that isgreater than zero.
 4. The method of claim 2, wherein the lowestaggregation level of CCEs with a respective number of candidates PDCCHsof the second type that is greater than zero is less than the lowestaggregation level of CCEs with a respective number of candidates PDCCHsof the first type that is greater than zero.
 5. The method of claim 1,wherein the UE determines the candidate PDCCHs of the first type using afirst search process in the first set of resources and determines thecandidate PDCCHs of the second type using a second search process in thesecond set of resources wherein the first search process is differentthan the second search process.
 6. The method of claim 5, wherein thefirst search process is the same as a third search process for candidatePDCCHs of a third type, and a UE decodes PDCCHs of the third type whenthe UE does not decode PDCCHs of the first type and of the second type.7. The method of claim 5, wherein the first search process in the firstset of resources includes a first random variable that is derived fromthe TTI and a UE identifier and the second search process in the secondset of resources includes a second random variable that is differentfrom the first random variable and is also derived from the TTI and theUE identifier.
 8. The method of claim 1, wherein the first set ofresources includes a first set of Physical Resource Blocks (PRBs), thesecond set of resources includes a second set of PRBs, a transmission ofPDCCH of the first type is distributed in multiple PRBs from the firstset of PRBs, and a transmission of a PDCCH of the second type islocalized in a single PRB from the second set of PRBs.
 9. The method ofclaim 1, wherein a PDCCH of the first type is transmitted only in thefirst set of resources in some TTIs and is transmitted either in thefirst set of resources or in a third set of resources in other TTIs,wherein the third set of resources is also signaled to the UEs by thebase station.
 10. The method of claim 1, wherein a number of resourceelements in a CCE used for transmitting a PDCCH of the second type isdifferent in different TTIs.
 11. A method for a User Equipment (UE) todetermine locations for M candidate Physical Downlink Control CHannels(PDCCHs) in a set of N Physical Resource Blocks (PRBs) in a TransmissionTime Interval (TTI), a candidate PDCCH including an aggregation level ofControl Channel Elements (CCEs), the M candidate PDCCHs being used for asame aggregation level of CCEs, the method comprising the steps of:determining a location for each of the M candidate PDCCHs in a differentPRB if N is greater than or equal to M; and determining a location foreach of the first N candidate PDCCHs in a different PRB and determininga location for each of the remaining if M-N candidate PDCCHs in adifferent PRB if M is greater than N and 2N is greater than or equal toH.
 12. The method of claim 11, wherein the location of each candidatePDCCH in a PRB from the set of N PRBs is determined by a function havinga first component that successively places candidate PDCCHs inrespective different PRBs from the set of N PRBs and a second componentthat places a candidate PDCCH within a PRB from the set of N PRBs aftera candidate PDCCH is placed by the first component in each PRB from theset of N PRBs and wherein for a PRB from the set of N PRBs the secondcomponent has a zero value if there is no previous candidate PDCCHplaced in the PRB and has a positive value if there is at least oneprevious candidate PDCCH placed in the PRB.
 13. The method of claim 11,wherein the second component equals zero when the first candidate PDCCHis placed in a PRB, is incremented when each subsequent candidate PDCCHis placed in the PRB, and places corresponding subsequent CCEs after theprevious CCEs corresponding to previous candidate PDCCHs in the same PRBand wherein if the last of the previous CCEs is the last indexed CCE inthe PRB, the first subsequent CCE is the first indexed CCE in the PRB.14. A method for a User Equipment (UE) to determine whether to includeor omit, for data reception, respective Resource Elements (REs) in areference Physical Resource Block (PRB) included in a Resource BlockGroup (RBG) signaled to the UE by a base station through a PhysicalDownlink Control CHannel (PDCCH) for reception of a Physical DownlinkShared Channel (PDSCH) in a Transmission Time Interval (TTI), thereference PRB belonging to at least one set of PRBs signaled to the UEby the base station for potential transmission of at least one PDCCH ina TTI, the method comprising the steps of: omitting, for data reception,REs in the reference PRB, if the PDCCH is of a first type and if the UEdetects the PDCCH in PRBs in a set of PRBs that includes the referencePRB, or if the reference PRB is in a first set of PRBs, regardless ofwhether the PRBs where the UE detects the PDCCH include the referencePRB, or omitting for data reception REs in the reference PRB if thePDCCH is of a second type and the UE detects the PDCCH in PRBs thatinclude the reference PRB; and including, for data reception, REs in thereference PRB if the PDCCH is of a first type, the reference PRB is in asecond set of PRBs, and the UE detects the PDCCH in PRBs in a first setof PRBs, or including, for data reception, REs in the reference PRB ifthe PDCCH is of a second type and the UE detects the PDCCH in PRBs thatdo not include the reference PRB.
 15. The method of claim 14, whereinthe set of PRBs where the UE detects the PDCCH of the first typeincludes 8 PRBs and the PDCCH of the first type is detected over 4 PRBsor wherein the set of PRBs where the UE detects the PDCCH of the firsttype includes 4 PRBs and the PDCCH of the first type is detected over 2PRBs.
 16. The method of claim 14, wherein the PDCCH of the first type isan interleaved PDCCH and the PDCCH of the second type is anon-interleaved PDCCH.
 17. A User Equipment (UE) apparatus forperforming decoding operations for two types of Physical DownlinkControl CHannels (PDCCHs), each including at least one Control ChannelElement (CCE) and transmitted from a base station in a Transmission TimeInterval (TTI), wherein a PDCCH of a first type is transmitted in afirst set of resources and with an aggregation level of CCEs selectedfrom a first set of aggregation levels of CCEs and wherein a PDCCH of asecond type is transmitted in a second set of resources and with anaggregation level of CCEs selected from a second set of aggregationlevels of CCEs, the apparatus comprising: a receiver for receivingsignaling from the base station informing of the first set of resourcesand the associated first PDCCH type and of the second set of resourcesand the associated second PDCCH type; a decoder for decoding for eachaggregation level of CCEs in the first set of aggregation levels of CCEsa respective number of candidate PDCCHs of the first type in the firstset of resources; and a decoder for decoding for each aggregation levelof CCEs in the second set of aggregation levels of CCEs a respectivenumber of candidate PDCCHs of the second type in the second set ofresources.
 18. The apparatus of claim 17, wherein, for at least oneaggregation level of CCEs, a respective number candidate PDCCHs of thefirst type is different than a respective number of candidates PDCCHs ofthe second type.
 19. The apparatus of claim 18, wherein the highestaggregation level of CCEs with a respective number of candidates PDCCHsof the first type that is greater than zero is greater than the highestaggregation level of CCEs with a respective number of candidates PDCCHsof the second type that is greater than zero.
 20. The apparatus of claim18, wherein the lowest aggregation level of CCEs with a respectivenumber of candidates PDCCHs of the second type that is greater than zerois less than the lowest aggregation level of CCEs with a respectivenumber of candidates PDCCHs of the first type that is greater than zero.21. The apparatus of claim 17, wherein the candidate PDCCHs of the firsttype are determined using a first search process in the first set ofresources and the candidate PDCCHs of the second type are determinedusing a second search process in the second set of resources wherein thefirst search process is different than the second search process. 22.The apparatus of claim 21, wherein the first search process is the sameas a third search process for candidate PDCCHs of a third type andwherein PDCCHs of the third type are decoded when PDCCHs of the firsttype and of the second type are not decoded.
 23. The apparatus of claim21, wherein the first search process in the first set of resourcesincludes a first random variable that is derived from the TTI and a UEidentifier and the second search process in the second set of resourcesincludes a second random variable that is different from the firstrandom variable and is also derived from the TTI and the UE identifier.24. The apparatus of claim 17, wherein the first set of resourcesincludes a first set of Physical Resource Blocks (PRBs), the second setof resources includes a second set of PRBs, a transmission of PDCCH ofthe first type is distributed in multiple PRBs from the first set ofPRBs and a transmission of a PDCCH of the second type is localized in asingle PRB from the second set of PRBs.
 25. The apparatus of claim 17,wherein a PDCCH of the first type is transmitted only in the first setof resources in some TTIs and a PDCCH of the first type is transmittedeither in the first set of resources or in a third set of resources inother TTIs wherein the third set of resources is also signaled by thebase station.
 26. The apparatus of claim 17, wherein a number ofresource elements in a CCE used for transmitting a PDCCH of the secondtype is different in different TTIs.
 27. A User Equipment (UE) apparatusfor determining locations for M candidate Physical Downlink ControlCHannels (PDCCHs) in a set of N Physical Resource Blocks (PRBs) in aTransmission Time Interval (TTI), a candidate PDCCH including anaggregation level of Control Channel Elements (CCEs), the M candidatePDCCHs being used for a same aggregation level, the apparatuscomprising: a searcher for determining a location for each of the Mcandidate PDCCHs in a different PRB if N is greater than or equal to Mand for determining a location for each of the first N candidate PDCCHsin a different PRB and determining a location for each of the remainingif M-N candidate PDCCHs in a different PRB if M is greater than N and 2Nis greater than or equal to M; and a decoder for decoding candidatePDCCHs.
 28. The apparatus of claim 27, wherein the location of eachcandidate PDCCH in a PRB from the set of N PRBs is determined by afunction having a first component that successively places candidatePDCCHs in respective different PRBs from the set of N PRBs and a secondcomponent that places a candidate PDCCH within a PRB from the set of NPRBs after a candidate PDCCH is placed by the first component in eachPRB from the set of N PRBs and wherein for a PRB from the set of N PRBsthe second component has a zero value if there is no previous candidatePDCCH placed in the PRB and has a positive value if there is at leastone previous candidate PDCCH placed in the PRB.
 29. The apparatus ofclaim 27, wherein the second component equals zero when the firstcandidate PDCCH is placed in a PRB, is incremented when each subsequentcandidate PDCCH is placed in the PRB, and places correspondingsubsequent CCEs after the previous CCEs corresponding to previouscandidate PDCCHs in the same PRB and wherein if the last of the previousCCEs is the last indexed CCE in the PRB, the first subsequent CCE is thefirst indexed CCE in the PRB.
 30. A User Equipment (UE) apparatus fordetermining whether to include or omit for data reception respectiveResource Elements (REs) in a reference Physical Resource Block (PRB)included in a Resource Block Group (RBG) signaled to the UE apparatus bya base station through a Physical Downlink Control CHannel (PDCCH) forreception of a Physical Downlink Shared Channel (PDSCH) in aTransmission Time Interval (TTI), the reference PRB belonging to atleast one set of PRBs signaled to the UE apparatus by the base stationfor potential transmission of at least one PDCCH in a TTI, the apparatuscomprising: a decoder for detecting the PDCCH; a selector for omittingfor data reception REs in the reference PRB if the PDCCH is of a firsttype and if the UE apparatus detects the PDCCH in PRBs in a set of PRBsthat includes the reference PRB or if the reference PRB is in a firstset of PRBs, regardless of whether the PRBs where the UE apparatusdetects the PDCCH include the reference PRB, or omitting for datareception REs in the reference PRB if the PDCCH is of a second type andthe UE apparatus detects the PDCCH in PRBs that include the referencePRB, and for including for data reception REs in the reference PRB ifthe PDCCH is of a first type, the reference PRB is in a second set ofPRBs, and the UE apparatus detects the PDCCH in PRBs in a first set ofPRBs or including for data reception REs in the reference PRB if thePDCCH is of a second type and the UE apparatus detects the PDCCH in PRBsthat do not include the reference PRB; and a receiver for receiving thePDSCH.
 31. The apparatus of claim 30, wherein the set of PRBs where thePDCCH of the first type is detected includes 8 PRBs and the PDCCH of thefirst type is detected over 4 PRBs or wherein the set of PRBs where thePDCCH of the first type is detected includes 4 PRBs and the PDCCH of thefirst type is detected over 2 PRBs.
 32. The apparatus of claim 30,wherein the PDCCH of the first type is an interleaved PDCCH and thePDCCH of the second type is a non-interleaved PDCCH.